5 Ocean water movements Surface circulationOcean currents are masses of water that flow from one place to anotherSurface currents develop from friction between the ocean and the wind that blows across the surfaceHuge, slowly moving gyres

8 Ocean water movements Surface circulationDeflected by the Coriolis effectTo the right in the Northern HemisphereTo the left in the Southern HemisphereFour main currents generally exist within each gyreImportance of surface currentsClimateCurrents from low latitudes into higher latitudes (warm currents) transfer heat from warmer to cooler areas

9 Ocean water movements Surface circulationImportance of surface currentsClimateInfluence of cold currents is most pronounced in the tropics or during the summer months in the middle latitudesUpwellingThe rising of cold water from deeper layersMost characteristic along west coasts of continentsBrings greater concentrations of dissolved nutrients to the ocean surface

11 Ocean water movements Deep-ocean circulationMost water involved in deep-ocean currents begins in high latitudes at the surfaceA simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean, through the Indian and Pacific Oceans, and back again

13 The coastal zone The land–sea boundaryShoreline – contact between land and seaShore – area between lowest tidal level and highest areas affected by storm wavesCoastline – the seaward edge of the coastBeach – accumulation of sediment along the landward margin of the ocean

15 Ocean water movements WavesEnergy traveling along the interface between ocean and atmosphereDerive their energy and motion from windPartsCrestTrough

16 Ocean water movements Waves Measurements of a waveWave height – the distance between a trough and a crestWavelength – the horizontal distance between successive crests (or troughs)Wave period – the time interval for one full wave to pass a fixed position

18 Ocean water movements Waves Wave height, length, and period depend onWind speedLength of time the wind blowsFetch – the distance that the wind travelsAs the wave travels, the water passes energy along by moving in a circleWaveform moves forwardAt a depth of about one-half the wavelength, the movement of water particles becomes negligible (the wave base)

20 Wave erosion Wave erosion Caused by Wave impact and pressureBreaks down rock material and supplies sand to beachesAbrasion – sawing and grinding action of water armed with rock fragments

21 Sand movement on the beachBeaches are composed of whatever material is availableSome beaches have a significant biological componentMaterial does not stay in one placeWave energy moves large quantities of sand parallel and perpendicular to the shoreline

22 Beaches and shoreline processesWave refractionBending of a waveWave arrives parallel to shoreResultsWave energy is concentrated against the sides and ends of headlandWave erosion straightens an irregular shoreline

24 Shoreline EvolutionShorelines are continually modified by erosional and depositional processes.Over time, a geologically stable coastline will become less jagged.Headlands erode…Creating sediments…Deposited in embayments…

25 Beaches and shoreline processesLongshore transportBeach drift – sediment moves in a zigzag pattern along the beach faceLongshore currentCurrent in surf zoneFlows parallel to the shoreMoves substantially more sediment than beach drift

32 Shoreline features Depositional featuresSpit – a ridge of sand extending from the land into the mouth of an adjacent bay with an end that often hooks landwardBaymouth bar – a sand bar that completely crosses a bayTombolo – a ridge of sand that connects an island to the mainland

33 Spit Elongated ridges of sand extending from the land into the mouth of an adjacent bay.

34 Aerial view of a spit and baymouth bar along the Massachusetts coastline

38 Shoreline EvolutionBecause shorelines are continually being modified, they are notoriously unstable in human terms.This creates problems because of intense development in the coastal zone.These problems result from erosion during…HurricanesNormal wave attack

39 Shoreline EvolutionBecause shorelines are continually being modified, they are notoriously unstable in human terms.This creates problems because of intense development in the coastal zone.These problems result from erosion during…HurricanesNormal wave attack

40 Shoreline Erosion Shoreline erosion is influenced by the local factorsProximity to sediment-laden riversDegree of tectonic activityTopography and composition of the landPrevailing wind and weather patternsConfiguration of the coastline

42 Stabilizing the shoreHard stabilization –Responses to erosion problemsTypes of structuresGroins – barriers built at a right angle to the beach that are designed to trap sandBreakwaters – barriers built offshore and parallel to the coast to protect boats from breaking wavesSeawalls – Armors the coast against the force of breaking wavesOften these structures are not effective

44 Responses to Shoreline ErosionGroinsBuilt to maintain or widen beaches.Constructed at a right angle to the beach to trap sand.Create erosion problems “downdrift.”

45 Responses to Shoreline ErosionSeawallBarrier parallel to shore and close to the beach to protect property.Stops waves from reaching the beach behind the wall.Results in…Destruction of beachesEnhanced damage when seawall is undermined and removed.Accelerating expenditures to rebuild bigger seawalls.

46 Stabilizing the shore Responses to erosion problemsAlternatives to hard stabilizationBeach nourishment by adding sand to the beach systemRelocating buildings away from beachErosion problems along U.S. coastsShoreline erosion problems are different along the opposite coasts

49 Stabilizing the shore Erosion problems along U.S. coastsAtlantic and Gulf CoastsDevelopment occurs mainly on barrier islandsFace open oceanReceive full force of stormsDevelopment has taken place more rapidly than our understanding of barrier island dynamics

50 Stabilizing the shore Erosion problems along U.S. coasts Pacific CoastCharacterized by relatively narrow beaches backed by steep cliffs and mountain rangesMajor problem is the narrowing of the beachesSediment for beaches is interrupted by dams and reservoirsRapid erosion occurs along the beaches

51 Coastal classificationShoreline classification is difficultClassification based on changes with respect to sea levelEmergent coastCaused byUplift of the land, orA drop in sea level

52 Coastal classificationClassification based on changes with respect to sea levelEmergent coastFeatures of an emergent coastWave-cut cliffsMarine terraces

64 Tides Tidal patterns Main tidal patterns Diurnal tidal patternA single high and low tide each tidal dayOccurs along the northern shore of the Gulf of MexicoSemidiurnal tidal patternTwo high and two low tides each tidal dayLittle difference in the high and low water heightsCommon along the Atlantic Coast of the U.S.

65 Tides Tidal patterns Main tidal patterns Mixed tidal patternTwo high and two low waters each dayLarge inequality in high-water heights, low-water heights, or bothPrevalent along the Pacific Coast of the U.S.

66 Tides Tidal patterns Tidal currentsHorizontal flow accompanying the rise and fall of tidesTypes of tidal currentsFlood current – advances into the coastal zoneEbb current – seaward-moving waterSometimes tidal deltas are created by tidal currents

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